Method of electroplating copper clad stainless steel cooking vessels



y 1951 H. J. LEE 2,560,966

METHOD OF ELECTROPLAT'ING COPPER CLAD TAINLESS STEEL COOKING VESSELS 2Sheets-Sheet 1 Filed July 31, 1947 mm V WYH IYMQ I nUefii/ m? raid JLee.

Ha mud Isl. J. LEE

Jul 17, 1951 4 2,560,966

METHOD OF ELE TROPLATING COPPER CLAD STAINLESS STEEL COOKING VESSELS 2Sheets-Sheet 2 Filed July 31, 1947 6mm 0 v In?) I 1 3273%: 3d 3142a,35%27M? Patented July 17, 1951 METHOD OF ELECTROPLATING COPPER CLADSTAINLESS STEEL COOKING VES- SELS .Harold J. Lee, Rome, N. Y., assignorto Revere Copper and Brass Inco a corporation of Maryla Application July31, 1947, Serial No. 764,956

Claims. 1 My invention relates to methods of cladding stainless steelcooking vessels with .an electrodeposited layer of copper. r Theinvention constitutes an improvement in the method and apparatusdisclosed in Kennedy,

Knight and Lee United States Patent 2,363,973 issued November 28, 1944to the assignee of this application, and in respect to the embodiment ofthe invention illustrated in the application drawings is particularlyuseful in claddin stainless steel cooking vessels by employment ofapparatus of the general type disclosed in pending Kennedy, Knight andLee application" Serial Number 630,266, filed November 23, 1945, nowPatent 2,506,794, dated May 9, 1950.

As disclosed by the patents above referred to, before electrodepositingon the stainless steel cooking vessel a cladding layer of copper thevessel is first treated for preparing it to receive such layer and causethe latter firmly to adhere thereto. Briefly, as described by saidpatents, such preliminary treatment consists in cleaning the surfaces ofthe vessel, when necessary, to remove grease, dirt and the like, thenpreferably roughening the cleaned surfaces, and treating them withelectrolytically released hydrogen While the surfaces are made a cathodein a dilute sulphuric acid bath. As further described by'said patents,upon competition of this preliminary treatment said surfaces aresubstantially immediately immersed in a copper plating bath in spacedopposed relation to a soluble copper electrode, the latter being made ananode and the vessel a cathode when said surfaces are so immersed forsubstantially immediately initiating deposition of the copper.

The surfaces of the vessel on which the layer of copper is to beelectrodeposited may be roughened by chemically etching them or by sandblasting. Best results, however, it has been found will be secured byetching them anodically. For etching them anodically the surfaces of thevessel on which the copper layer is to be subsequently electrodepositedmay be immersed inan electrolytic bath consisting of water containingfrom about 8.5 to 62%, preferably about 30%, by weight of sulphuricacid. The bottom portion of the vessel immersed in this electrolyte withits bottom surface in spaced relation to an insoluble electrode such aslead, the electrode being made a cathode and the vessel an anode so asto plate off the exterior surface of the immersed portion of the vesselwhen current is passed. Best results will be secured with: currentdensities of from 300 to 350 amperesper square foot of anode will beelectrolyzed rporated, Rome, N. Y., nd

surface, although smaller and larger densities, say from to 550 amperesper square foot, may be employed. The current is passed until thesurface is suificiently etched to begin to show a socalled satinsurface.

Preferably just as soon as the vessel begins to show the satin surfaceabove referred to it is removed from the electrolyte, immediately rinsedwith water, and its roughened surfaces placed in a second electrolyteof, the same composition above referred to with its bottom surface inspaced relation to an insoluble electrode such as lead, this electrodebeing made an anode and the vessel a cathode. When current is passed theelectrolyte to liberate nascent hydrogen which is plated on theroughened surfaces of the vessel, whereupon the vessel is removed fromthe electrolyte and immediately rinsed with water and placed in thecopper plating bath in spaced opposed relation to the soluble copperelectrode and electrodeposition of copper immediately initiated bymaking the electrode an anode and the vessel a cathode as abovedescribed. If the surfaces of the vessel'are roughened by sand blastingor chemical etching they are preferably immediately rinsed with .water,and. placed in the electrolyte for treating them cathodically withelectrolytically released hydrogen, as just explained. Preferably muchlower current densities are employed when the vessel is made a oath odeas compared to when 'it is made an anode. When it is a cathode currentdensities of from 40 to 400 amperes per square foot of cathode surfacemay be employed. g

The same electrolyte may be employed for treating the vesselcathodically as that employed for treating it anodically, in which casethe vessel will be first/treated anodically and then the polarity of theelectrical connections to the vessel and electrode will be reversed tomake the vessel a cathode and the electrode an anode. For reversing thepolarity there may be employed the familiar double-throw two-poleswitch, aresistance being thrown into circuit with the vessel when it isthe cathode for reducing the current density to the desired value.Preferably, however, to prevent undue contamination of the electrolytewhich treats the vessel cathodically, sepa-. rate electrolytes areemployed for the anodic and cathodic treatments. 6 In the apparatusdisclosed by Patent 2,363,973 above referred to the bottom and adjacentside wall portions of the vessel are immersed in the electrolyte and thevessel axially rotated with the bottom in spaced coaxial relation to afiat electrode. Applicant has found that with such an arrangement thetimes of both the anodic and cathodic treatments to secure satisfactoryresults are unduly prolonged, and that as a result of the cathodictreatment with such an arrangement poor adherence of the subsequentlyelectrodeposited copper layer is liable to result particularly when highcurrent densities are employed for speeding up the cathodic treatment.He has however found that these defects may be eliminated by employingfor the electrode one having a convex surface which is substantially asurface of revolution, and placing the vessel in coaxial relationtherewith with the bottom of the vessel opposed to said surface.

Applicant believes that with the flat electrode the current passingbetween it and the vessel is non-uniformly distributed, the minimumcurrent being at the center of the bottom of the vessel and the maximumcurrent being at the edge portions of said bottom and adjacent sidewalls of the vessel, while with the electrode having the convex surfacethe current density is approximately uniform over the entire immersedportion of the vessel. For example, he believes that with a flatelectrode, when the total current flowing is say 250 amperes, there maybe a current density of say only 100 amperes per suqare foot at thecenter portion of the bottom of the vessel and a current density of say900 amperes per square foot at the extreme edge portions of said bottom.The time necessary to treat any portion of the immersed surfaces of thevessel satisfactorily will depend upon the current density at thatportion, the greater the current density the less the time. Consequentlywhen a flat electrode is employed, and the current density is a minimumat the center portion of the bottom of the vessel, the time for treatingthe vessel satisfactorily will depend upon the time it takes to treatthat portion satisfactorily. When the convex electrode is employed thistime will be much reduced, because for any total current flowing thecurrent density at the center portion of the vessel is increased at theexpense of the current density at the edge portions, making the currentdensity approximately uniform over the entire surface of the, bottom ofthe vessel, as above explained. Applicant has found that to some extenta uniform distribution of the current over the immersed portions of thevessel may be secured by using a flat electrode with an annular shieldinterposed between the edge portions of the vessel and the electrode.However, such a shield will be suitable for but one diameter of vessel,and a shield of different size must be substituted for each diameter ofvessel. However, the electrode having the convex surface is adapted foruse with any diameter of vessel, because the greater the diameter of thevessel the farther are its edge portions away from the surface portionof the electrode immediately below it.

In respect to improved adherence of the electrodeposited layer of copperon the stainless steel surfaces treated cathodically by use of theconvex electrode, applicant believes that when av fiat electrode isemployed, and the acid electrolyte is contaminated with even minutetraces of a heavy metal, minute practically microscopic quantities ofsuch metal are electrodeposited on the edge portions of the immersedsurfaces of the vessel when it is being treated cathodically withelectrolytically released hydrogen, this resulting because of the highcurrent density at said portions and the relatively prolonged timenecessary for treating the immersed surfaces as above described, thisdeposit of metal because of the high current density being spongy sothat it prevents the subsequently electrodeposited layer of copper fromsatisfactorily adhering to thestainless'steel. When the electrode havingthe convex surface is employed, however, the current at the edgeportions of the immersed surfaces of the vessel and the time necessaryto treat those surfaces are reduced as above explained, with the resultthat no appreciable quantities of heavy metal will be deposited on thesurfaces, or, even assuming they were deposited, would not be spongy.

Suitable apparatus according to the invention for performing the abovemethod is shown in the accompanying drawings, in which:

Fig. 1'is a transverse section of apparatus for treating the vesseleither cathodically or anodically;

Figs. 2, 3 and 4 are, respectively, sections on the lines 2-2, 3--3 and4-4 of Fig. l, with parts omitted and parts broken away, Fig. 4 being ona reduced scale;

Fig. 5 is a plan of the apparatus according to Fig. l; r

Fig. 6 is a section on the line 66 of Fig. 1, with parts omitted andparts broken away; and

Figs. 7, 8 and 9 are, respectively, sections on the lines 1-'I, 8-8 and9-9 of Fig. 5, with parts omitted and parts broken away.

Referring to the drawings, the electrolyte is contained in an open toptank having a bottom I, side walls 3 and end walls 5, this tank beingpreferably formed of steel and interiorly coated, as indicated at I,with lead, rubber, or other material inert with respect to theelectrolyte.

Interiorly of the tankis positioned a flat horizontal bar 9 of copperextending in spaced relation to the bottom of the tank'from adjacent oneend wall 5 thereof to the other. At each of opposite ends this bar isshown as supported in an adjacent block ll of insulating material, theblocks resting upon and being secured by bolts It. to the lower portion[5 of an inverted U-shaped bracket. As shown, H of the bracket have endflanges I9 resting upon the outwardly projecting flanges 2| of theadjacent side walls of the tank, to which flanges 2| said flanges is aresecured by bolts 23. The U-shaped bracket, like the tank, also ispreferably coated with lead, rubber, or the like.

At one end the bar 9 is provided with an upwardly extending portion 25,which portion at its upper end is bent outwardly, as shown at 21, andrests upon and is brazed to a bar 29 of conductive material such ascopper. Brazed to the bar 29 adjacent one of its ends is a connector 31for a cable 33. The bar 29, as shown, rests upon a strip 35 ofinsulating material, and is secured to the outwardly extending; flange31 of the adjacent end wall of the tank by bolts 39 extending throughsaid flange and. strip and tapped into the bar, a flanged bushing 4|surrounding, the bolt insulating it from the flange.

As shown, carried by the bar 9 are upwardly projecting, brackets 43having lower flanges 45 brazed to the upper surface of the bar. At theirupper ends each bracket has a flange 41 to pairs of which are brazed,soldered or welded the edge portions of disk-like electrodes 49. Eachelec-' trode is in the form of a sheet oflead, or other conductivematerial insoluble in the electrolyte; shapedto present an upper surfaceit whicnis the opposite legs approximately a segment of a sphere. Asshown, each electrode is formed with perforations 53 distributed'thereover in relatively closely adjacent relation. When the cookingvessels are placed above the electrodes and rotated as hereinafterdescribed electrolyte is drawn through the perforations from beneath theelectrodes and forced radially outwardly through the spaces between theelectrodes and bottoms of the vessels, the rapid circulation of theelectrolyte thus .caused permitting the use of high current densitieswithout burning of the immersed surfaces, of the vessels. Preferably thebar 9, the

.upwardly extendin portion 25 of that bar, and

the brackets 43 have a coating 55 of lead to .protect them from thecorrosive action of the electrolyte, or, if desired, may be coated withrubber for that purpose and for insulating them from the electrolyte.

At the opposite end of the tank from the bar 29 the'outwardly projectingupper flange 51 of the tank end wall carries a second bar 59 of copperto which is brazed a connector SI for the cable 63. Interposed betweenthe bar 59 and the flange 51 is a strip 65 of insulating material, thebar 59 being secured to the flange by bolts 61 extending through theflange and strip and tapped into the bar. For insulating the bolt fromthe flange is provided a flanged insulating bushing 69 through which thebolt extends.

Supported in the tank above each electrode 49 in coaxial relationtherewith is shown a cooking vessel V having a flat bottom Wall II andside walls 13, the latter includin the rounded portions I5 at the cornerbetween the side walls and the bottom. In practice the tank ordinarilywill be filled with electrolyte to about a level L, and with a smallercooking vessel as, for example, that illustrated at 22, the tank will befilled with electrolyte to about a level Z, in each case to cause thelower portion of the vessel to be immersed to just above the top of itsrounded corner portion I5. It will be understood, however, that thevessel may have a square corner,

and that whether the corner is square or rounded the depth of immersionof the vessel will depend upon the portion thereof to be clad withcopper after it is removed from the tank. Satisfactory results, it hasbeen found, will be secured by having minimum spacing between the bottomof the vessel and the electrode about three-quarters of an inch and thedepth of immersion of the vessel not exceeding two and one-half timesthat distance, although such spacing and the depth of immersion are notI critical. Satisfactory results will be secured in treating vesselshaving diameters of from 4 to 15 Inches with electrodes 18 inches indiameter, the upper surface of the electrode being a segment of asphereof about 21 inches radius resulting in the circumferential edge of thetop surface of the electrode being about 2 inches below its centerportion. With such radius of curvature the current density, it has beenfound, is approximately uniform over the entire surface of the vessel.However, the radius of curvature is not critical, as a markedimprovement in current density distribution is noted with other radiicausing the upper surface of the electrode to be convex. In fact suchimprovement will be secured when its convexity is presented by a conicalsurface of the same ratio of diameter to altitude as the sphericalsurface, and a conical surface will for some reason give even betterresults than will a spherical surface with vessels depending portions 83screw 9I.

of from 4 to '7 inches in diameter. the diameter of the electrode shouldnot be less than about 1 to 1 inches greater than the diameter of thevessel, and having the electrode radius not less than the radius of thevessel plus the depth of immersion of the vessel will satisfy thiscondition.

As shown, the vessels V are supported by a carrier comprising the spacedbars 11 which are preferably formed of metal such as brass and areintegrally connected at their ends by cross-bars 19. As shown, at theintermediate portion of the carrier are cross-bars BI integrally formedwith the side bars TI. These cross-bars BI have which are perforated forfixedly carrying elongated vertical sleeves 85, in which latter arerotatably mounted vertical shafts 81. As shown, carried by the lower endof each shaft 8? is a sleeve '89 (Fig. 7) secured thereto by a set screw9I, the sleeve projecting beyond the lower end of the shaft 31 forreceiving the upper end of a, shaft 93, the latter being removablysecured to the sleeve by a second set Carried by the lower end of eachshaft 93 is a chuck for supporting the cooking vessel. This chuck, whichis preferably formed of resilient sheet copper, has a bottom 95 to whichthe shaft 93 is joined, as by welding, and has side walls formed withV-shaped splits 91 to form a circular series of spaced resilient prongs99, the latter for engaging the lower portions of the inher side wallsurfaces of the vessel for supporting it and detachably connecting it tothe shaft .33.

As shown, each shaft 81 is provided at its upper end with a bevel gearIllI meshing with a bevel gear I 93 on a horizontal shaft l rotatablysupported in bearing-s I01 on the carrier crossbars 8|. For driving theshaft I05 it is shown as connected by an insulating coupling I09 to thedriven shaft I m of an electric motor, I I I, the mo- In general torbeing supported on a plate M3 of insulating ing upon and secured byrivets or the like I23 (Fig. 3) to an insulating strip I25, the barsadjacent one end being connected by leads I21 to a source of currentsupply. As shown, the strip I25 at opposite ends is secured to andsupported on brackets I29 carried by the adjacent end wall 5 of thetank. These brushes are of a known type in which the contact portions IIii are yieldingly extensible relative to the bodies of the brushes soas to make good contact with the bars I2I when the carrier for thevessels is placed in position.

As shown, when the carrier is placed on the tank the lower contactportion I 3i (Fig. 8) of the cross-bar I33, which latter is formedintegrally with the side bars 'I! of the carrier, rests upon the bar 59connected to one side of the line by the cable 63. This will place thevessels in electrical communication with the cable 63 by way of theconnector 6|, cross-bar I33, side bars I'!, cross-bars 8|, dependingportions 83 of the latter, sleeves 85, shafts 87, sleeves '89, shafts'93, and the chuck-s having the portions 99 which engage the vessel. Atthe same time the electrodes 49 will be placed in communication with thecable 33 connected, as above explained, to the opposite side of theline. For supporting the end of the carthe copper on them.

escapee electrodes 59 are cathodes, and that when the roughened surfacesof the vessel are treated with electrolytically released hydrogen thecables are rier opposite the cross-oar I33, when the carrier "is placedon the tank, the cross-bar is at that end so connected that the vesselsare cathodes and the electrodes are anodes. As above explained,

the vessels are preferably treated anodicall and catho'dically inseparate tanks. In practicethe vessels will be placed on thechucks'before the carrier is placed on the tank, the carrier preferablybeing supported on a suitable rack forcthat purpose, then by use of asuitable conveyor, preferably one of the swinging arm type of knownconstruction, the carrier is removed from the rack and placed on thetank for treating the vessel anodically, then, at the end of the anodictreatment, by use of a second conveyer, preferably of the same type, thecarrier is lifted and immediately placed on the tank for treating thevessel cathodically, and at the completion of the cathodic treatment thecarrier is lifted by a conveyer of the same type and placed on the tankfor electrodepositing copper on the c'athodically treated portion of thevessel, which last men tioned tank may be of the type described in theabove mentioned Patent 2,506,794 according to which the tank has solublecopper anode elec trodes immersed in the electrolyte, in spaced opposedrelation to which electrodes the bottoms of the cathodically treatedvessels are placed and the vessels made cathodes for electrodepositingFor permitting such movement of the carrier from tank to tank thecarrier is shown as provided at each of opposite ends with a projection54! for engagement by the conv'eyer, suitable provision being made, forexample having the projection of insulating material, to preventgrounding of the vessel during its travel from the tank in which it istreated cathodically to the tank in which the copper iselectrodeposited, as grounding of the vessel apparently acts todissipate the film of hydrogen placed on the surfaces of the vesselduring the cathodic treatment, or acts to destroy the efliciency of thatfilm if not dissipated.

It will be understood that within the scope of the appended claims widedeviations may be made from the method described without departing fromthe spirit of the invention.

I claim:

1. In a method of coating the substantially flat bottom and adjacentside wall surfaces of revolution of a stainless steel cooking vesselwith a strongly adhering layer of electrodeposited copper, the steps ofimmersing said surfaces ina dilute sulphuric acid bath with said bottomsurface in opposed spaced substantially coaxial relation to the convexsurface of revolution of an insoluble electrode of greater diameter thanthe diameter of the vessel and of material altitude, making said vessela cathode and said electrode an anode while immersed in said bath fortreating said surfaces of the vessel with electrolyticall'y releasedhydrogen, and upon cessation of such treatment removing said vessel fromsaid bath and substantially immediately immersing said surfaces thereofin a copper plating bath in opposed spaced relation to a soluble copperelectrode and. making the latter an anode and the vessel a cathode.

2. In the method according to claim 1 axially rotating the vessel whileit is a cathode in both instances.

3. In the method according to claim 1 the step of roughening the saidsurfaces of the vessel prior to treating them with the electrolyticallyreleased hydrogen.

4. In the method according to claim 1 the steps of roughening the saidsurfaces of the vessel, prior to treating them with the electrolyticallyreleased hydrogen, by immersing said surfaces in a dilute sulphuric acidbath with the bottom surface of the vessel in opposed spacedsubstantially coaxial relation to the convex surface of revolution of aninsoluble electrode of greater diameter than the vessel and of materialaltitude, and making the vessel an anode and said electrode a cathodewhile immersed in said bath.

5. In the method according to claim 1 the steps of roughening the saidsurfaces of the vessel, prior to treating them with the electrolyticallyreleased hydrogen, by immersing said surfaces in a dilute sulphuric acidbath with the bottom surface of the vessel in opposed spacedsubstantially coaxial relation to the convex surface of revolu tion ofan insoluble electrode of greater diameter than the vessel and ofmaterial altitude, making the vessel an anode and said electrode acathode while immersed in said bath, and axially rotating the vesselboth when it is an anode for toughening it and when it is a cathode fortreating it with hydrogen.

l-IAROLD J. LEE.

REFERENCES CITED The followingreferences are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES The Metal Industry, London, April28, .1944; pages 266-367, an article by Leadbeater.

1. IN A METHOD OF COATING THE SUBSTANTIALLY FLAT BOTTOM AND ADJACENTSIDE WALL SURFACES OF REVOLUTION OF A STAINLESS STEEL COOKING VESSELWITH A STRONGLY ADHERING LAYER OF ELECTRODEPOSITED COPPER, THE STEPS OFIMMERSING SAID SURFACES IN A DILUTE SULPHURIC ACID BATH WITH SAID BOTTOMSURFACE IN OPPOSED SPACED SUBSTANTIALLY COAXIAL RELATION TO THE CONVEXSURFACE OF REVOLATION OF AN INSOLUBLE ELECTRODE OF GREATER DIAMETER THANTHE DIAMETER OF THE VESSEL AND OF MATERIAL ALTITUDE, MAKING SAID VESSELA CATHODE AND SAID ELECTRODE AN ANODE WHILE IMMERSED IN SAID BATH FORTREATING SAID SURFACES OF THE VESSEL WITH ELECTROLYTICALLY RELEASEDHYDROGEN, AND UPON CESSATION OF SUCH TREATMENT REMOVING SAID VESSEL FROMSAID BATH AND SUBSTANTIALLY IMMEDIATELY IMMERSING SAID SURFACES THEREOFIN A COPPER PLATING BATH IN OPPOSED SPACED RELATTION TO A SOLUBLE COPPERELECTRODE AND MAKING THE LATTER AN ANODE AND THE VESSEL A CATHODE.